Monday, May 04, 2009

Fermi Pokes A Hole In ATIC Balloon

OK, OK... no more puns! :)

ScienceNow is reporting from the APS April Meeting that a new result from Fermi Gamma-ray Space Telescope may have damper the enthusiasm of a possible detection of dark matter that was reported from ATIC balloon experiment.

One way to spot these particles might be to look to the skies. Some popular theoretical models suggest that if two lingering particles of dark matter collide, they should annihilate to create an ordinary particle and an antiparticle, such as an electron and a positron, which can be observed. Those particles should emerge with a definite energy determined by the mass of the dark energy particles, leading to a sharp peak in the energy spectrum of electrons and positrons from space.

That's why the results from the NASA-funded Advanced Thin Ionization Calorimeter (ATIC) balloon experiment sparked interest last fall (Science, 21 November 2008, p. 1173). ATIC observed that the number of electrons and positrons hitting Earth peaked sharply between about 300 billion and 800 billion electron volts. That dramatic excess appeared to be consistent with dark-matter annihilations.

But the new satellite measurements, from the $690 million Fermi telescope, don't reveal such an excess. Launched in June and designed to detect high-energy photons called gamma rays, Fermi is actually a sophisticated particle detector that serves just as well to detect electrons and positrons. It detected more than 4 million electrons and positrons from August through January--compared with ATIC's thousands--and Fermi researchers precisely measured the particles' energy spectrum.

So now they have to reconcile the two contradictory observations. And of course, there's PAMELA to content with.

Edit: Here's a more detailed coverage of this, AND, with a free download of the relevant paper.


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